Trimmer condenser



July 19, 1949.

J. D. REPKO 2,476,385

TRIMMER CONDENSER Filed April 15, 1946 ATTORNEY Patented July 19, 1949 2,476,385

TRIMMER CONDENSER Jan Dirk Bepko, Eindhoven, Netherlands, as-

lignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 15, 1946, Serial No. 662,131 In the Netherlands December 27, 1843 Section 1, Public Law 690, August 8, 194.6 Patent expires December 27, 1963 3 Claims. (01. 175-415) This inventiongrelates to a trimmer condenser having an air dielectric and comprising concentric cylindricallylbent electrodes. The term trimmer condenser is to be understood to mean a condenser having a maximum capacity of the order of magnitude of pf.

Trimmer condensers, also referred to as trimmers, must not only have small dimensions but particularly for uses at very high frequencies, also the same satisfactory properties as normal variable condensers. In the well-known constructions this has been insufllciently recognized or it,

has been impossible to fulfill these requirements.

Among the various constructions of trimmer condensers those having an air-dielectric and concentric cylindrically bent electrodes take a prominent place by reason of their comparatively satisfactory properties. The air dielectric has the efiect of reducing the dielectric losses. Cylindrically bent electrodes are mechanically resistant and their concentric arrangement ensures a certain insensibility of the capacity to small relative displacements of the electrodes in a direction normal to the cylinder axis.

This invention provides a new construction for a trimmer condenser in which many disadvantages inherent in prior art constructions are avoided and in addition some advantages are secured.

According to this invention, the movable electrode is arranged so as to be slidable relatively to the stationary and the screw as well as its attachment members are arranged entirely on that side of the movable electrode which is remote from the stationary electrode. It is found that due to sliding movement and the emcient arrangement of the screw the capacity variation per degree of angular rotation is quite uniform. In addition, it is possible to eliminate the backlash by means of a spring which forces the movable electrode towards one end. In the well-known construction it is impossible to fit such a spring in a simple manner, the movable electrode also performing a rotation. The construction according to the invention thus introduces accurate adjustability of the trimmer condenser.

In order that the invention may be clearly understood and readily carried into efiect it will now be described more fully with reference'to the accompanyng drawing, in which Fig. 1 is a plan of a trimmer condenser according to the invention.

Fig. 2 is a sectional view thereof taken on the line 11-11 of Fig. 1. The plan shown in Fig. 1 is viewed here as indicated by the arrows 1-1.

condenser.

The Figures show the trimmer condenser in the correct proportion, the length of line a corresponding with 1 cm.

Referring to the figures, l and 2 designate the concentrically arranged. cylindrically bent electrodes. The electrode I is secured to an insulating rod 3, the latter being pressed into a central bore of the electrode. In the present instance the rod is cylindrical and made of ceramic material. It acts as a, guide for the movable electrode 2. The frame of the trimmer condenser is formed by end plates 4 and 5 which are interconnected by draw rods 6 and 1 by means of a lap joint. The insulation rod 3 is pressed in a bore of the end plate 4. The end plate 5 has formed in it a, threaded bore in which the screw 8 is adapted to rotate. Undue movements of this screw are avoided by a spring plate 8 which is also threaded and brings about a resilient pinching enclosure of the screw 8. The screw 8 is provided at its end with a ring III which avoids entire turning out of the screw. In addition, the end of the screw has formed in it a cavity ii in which a ball l2 bears. The latter is made of insulating material, for example ceramic material. The

' other side of the ball I! is in contact with the plane part ii of a hood I which is rigidly connected to the movable electrode 2. The spring i5 urges the movable electrode as far as possible to the right and hence against the bore l2. The electrode 2 and the hood I have rigidly fitted between them a plate I 8 which is shown in dotted lines in Fig. 1. This plate has a forked extension I! which clasps a circular ceramic rod l8 which is secured to the end plate It. The head .of the screw 8 is square and comprises a saw-notch so that it can be turned by means of a wrench to match equally well as by means of a screw driver. The stationary electrode I has a soldering tag 20 secured to it. The movable electrode 2 is connected, by means of a flexible conductor 2|, to a soldering tag 22 secured to the insulating rod i8. The trimmer is secured to the plate 25 by screws 23 and 24. Thus, turning the screw 8 does not result in any deformation of the frame.

The position of the movable electrode can be changed by rotation of the screw 8. It is obvi-- ous that accurate adjustability is thus ensured. The change in capacity per degree of angular rotation does not exhibit any unevennesses. The capacity variation of the trimmer condenser shown is consequently constant throughout the entire change of the capacity.

By making the draw rods 6 and 1 of a suitably chosen metal the temperature coefllcient of the capacity may be rendered negative. This is advantageous since it permits of neutralizing or else reducing the frequently occurring positive temperature coeflicient of condensers connected in parallel or in series with the trimmer condenser.

Owing to the favourable arrangement of, the screw the electrical lines of force practically do not pass through the ceramic material. This ensures a very low zero capacity and also low losses.

The movable and the stationary electrodes of the trimmer condenser shown are both insulated from the frame. A so-called anti-radiation construction is thus obtained. This is also possible in a manner difierent from that shown. Thus, for example, it is possible to provide one of the rods 6, 'l with an insulating layer or to surround it by an insulating tube and to cause the forked extension I! to clasp it. This permits of trimming being effected simply with metal tools, such 7 as a normal screw driver or wrench, without any hand effect occurring, also as a result of the screening effect of the plate 5.

If this anti-radiation construction is not essential, the ball l2 may be made of metal and the draw rod 6 or I may be used without insulating coating ,in order that rotation of the movable electrode may be avoided with the aid of the forked extension H.

The trimmer condenser shown has a zero capacity of 2 pf. and a maximum capacity of pf. The total change in capacity corresponds with an angle of rotation of the screw 8 of 3000. It is only natural that the zero capacity and the maximum capacity can both be reduced by removing parts from the cylindrically bent electrodes I and 2.

What I claim is:

l. A trimmer condenser having an air dielectric comprising a pair of cylindrical concentric electrodes one of which is stationary and the other of which is movable, a centrally disposed 'fixed insulating rod for guiding the movement ,4 tric comprising a pair of cylindrical concentric electrodes one of which is stationary and the other of which is movable, a centrally disposed fixed insulating rod for guiding the movement of the movable electrode, a movable support for said movable electrode, a' main supporting structure, a stationary guide rod secured thereto, a fork rigidly secured to the movable electrode and adapted to slide along the stationary guide rod, a hood on and movable with the movable support and the movable electrode, a compressible spring in the hood and pressed against an end of the fixed insulating rod which guides the movement of the movable electrode, and a centrally disposed adjusting screw engaging the side of the hood remote from the insulating rod.

3. A trimmer condenser having an air dielectrio comprising a pair of cylindrical concentric electrodes one of which is stationary and the other of which is movable, a centrally disposed insulating rod for guiding the movement of the movable electrode, a movable support for said movable electrode, a main supporting structure comprising a pair of end plates and a pair of connecting rods arranged symmetrical to and parallel with said insulating rod which guides the movement of the movable electrode, a stationary guide rod secured to one of said end plates, a fork rigidly secured to the movable electrode and adapted to slide along the stationary guide rod, a hood on and movable with the movable support and the movable electrode, a compressible spring in the hood and pressed against an end of the fixed insulating rod which guides the movement of the movable electrode, and a centrally disposed adjusting screw extending through an aperture in one of said end plates which engages the side of the hood remote from the insulating rod, said connecting rods of said main supporting structure having a temperature coeflicient of expansion for which the temperature coefiicient of capacity of said condenser is negative.

JAN DIRK REPKO.

REFERENCES ClI'lllElD The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,281,147 Franklin Apr. 28, 1942 FOREIGN PATENTS Number Country Date 108,801 Australia Apr. 15, 1938 

